The inventors have recently published reports that have enucleated and explained the unusual "vapochromic" changes in absorption and emission spectra that result when certain stacked platinum complexes are exposed to organic vapors; see, e.g., C. L. Exstrom et al, Chemical Materials, Vol. 7, pp. 15-17 (1995) and C. A. Daws et al, Chemical Materials, Vol. 9, pp. 363-368 (1997).
A typical experiment involves a solution, crystal or solid film of material, such as tetrakis(p-decylphenylisocyano)platinum tetracyanoplatinate (I) (see FIG. 1, which depicts the chemical formula of the compound, where the dashed vertical line indicates the c-axis) that forms stacks of alternating cations and anions with strong inter-platinum interactions. These salts exhibit an intense absorption band in the visible region. Exposing the stacks to small molecule vapors, such as acetone or chloroform, leads to sorption of the vapor molecules in the free volume between the stacks, and produces shifts in the absorption and emission spectra. These "vapochromic" or "vapoluminescent" changes are usually reversible so that the original spectrum is regained quickly after the vapor is removed. Such an effect has potential application for sensor technology.
Molecular LEDs are under intense investigation; see, e.g., R. H. Friend in Conjugated Polymers and Related Materials, W. R. Salaneck et al, Eds., Chapter 22, Oxford University Press (1993); A. J. Heeger, in Conjugated Polymers and Related Materials, W. R. Salaneck et al, Eds., Chapter 4, Oxford University Press (1993); R. H. Friend et al, in "Physical Properties of Polymers Handbook", J. E. Mark, Ed., AIP Press, New York (1996); Y. Yang, MRS Bulletin, pp. 31-38 (June 1997); T. Tsutsui, MRS Bulletin, p. 39-45 (June 1997); and W. R. Salaneck et al, MRS Bulletin, p. 46-51 (June 1997). However, to the best of the inventors' knowledge, there is only one unspecific report from the patent literature which describes this type of LED sensor; see, U.S. Pat. No. 5,629,533, issued to D. E. Ackley et al May 13, 1997.
Vapochromic platinum complexes and salts have been the subject of a patent; see, U.S. Pat. No. 5,766,952, issued to Kent R. Mann et al on Jun. 16, 1998. Such complexes change color when exposed to certain organic vapors.